This invention relates to the processing of electronic components and assemblies, and in particular to the reflow of solder and cleaning of the components.
The manufacture of electronic assemblies and components commonly involves the mounting of individual electronic devices, such as transistors, integrated circuits, resistors and the like on pre-printed circuit boards. The assemblies and components are then reflowed and often cleaned.
The manufacture of Ball Grid Array (BGA) components and assemblies commonly involves the mounting of solder balls or prepared spheres on pre-printed circuit boards or substrates on the bottom surface of an integrated circuit, such as a so-called flip chip. In a typical process, the circuit boards and substrates will be processed through a line of machines which include a magazine unloader, a ball mounter, an inspection machine, a 1 to 3 converter, a reflow apparatus, a cleaning apparatus, a 3 to 1 converter and a magazine loader. These machines take considerable floor space and limit the production line that can be utilized in a given amount of relatively expensive floorspace. After mounting, reflow and cleaning, the BGAs become the input/output paths for electron flow to the next level assembly.
Since most assembly of BGA components and assemblies is performed in a clean room environment with very expensive floor space costs, there is an ongoing need to conserve floorspace. Thus, it would be of great benefit to provide greater efficiency to the manufacturing process and to reduce the required floor space for the manufacturing process.
In accordance with one aspect of the present invention, an apparatus is providing for processing electronic components which travel along first and second conveyors in a pre-determined direction. The apparatus includes a frame contained in unitary housing. A reflow assembly is mounted on the frame within the unitary housing and has a reflow conveyor conveying the electronic component from the first conveyor in a reflow direction non-parallel to the pre-determined direction to reflow solder on the electronic component. The apparatus also has a cleaning assembly mounted on the frame also within the unitary housing and has a cleaning conveyor conveying the electronic component from the reflow conveyor in a cleaning direction generally opposite to the reflow direction to clean the electronic component and deliver the electronic component to the second conveyor.
In accordance with another aspect of the present invention, the reflow direction and cleaning direction are perpendicular to the pre-determined direction.
In accordance with another aspect of the present invention, a unitary compact reflowing and cleaning apparatus is provided and is specially suited for the reflowing and cleaning of BGA components of silicon chips which are manufactured in either strip form or individually held in JEDEC type trays, boats or carriers, in contrast to the typically larger sized printed circuit boards for which most of the present commercial reflow ovens and cleaning devices are designed.
In yet another aspect of the present invention through the use of selective blower manipulation and the utilization of negative pressure, a reflow oven and cleaner may be housed within a unitary housing without the risk of contamination of one process by the other process taking place within that same unitary housing.
In accordance with yet another aspect of the present invention, the cleaning portion of the apparatus operates with a cleaning fluid at a temperature more elevated than is typical with present commercial cleaners. The heightened temperature of the fluid within the cleaning apparatus minimizes the temperature difference between strips or trays exiting the reflow portion of the apparatus and allows a reflow and cleaning more rapidly than with the typical present day installations. This is because, in the apparatus of the present invention, the BGA components or chips contained in the strips or in JEDEC trays, boats or carriers, do not cool down as much and therefore can be cleaned sooner since they are cleaned prior to reaching room temperature and before typical contaminants present after reflow fully solidify or cure.
In accordance with yet another aspect of the present invention, the reflow portion of the apparatus of the present invention utilizes IR heating to rapidly reflow the BGA components or other chips in either strip form or held in JEDEC trays, boats or carriers. Convection or conduction heating may alternatively be used.
In accordance with a further aspect of the present invention, the reflow and cleaning apparatus is equipped with a convection-type reflow heating system. The convection-type reflow heating system is disposed in the reflow assembly portion of the reflow and cleaning apparatus and comprises a number of zones including an entry isolation zone disposed at the entry point of the reflow convener, at least one reflow heating zone disposed adjacent to the entry isolation zone, a reflow-to-cooling zone disposed adjacent to the reflow heating zone, a cooling zone disposed adjacent to the reflow-to-cooling zone, and an exit isolation zone disposed adjacent to the cooling zone and at the exit point of the reflow conveyor. The convection heating system also includes a air or inert gas distribution system disposed in the reflow assembly for delivery and recirculation of heated air or gas to the reflow heating zone and delivery of cool air or gas to the cooling zone. The air or inert gas reflow and cooling temperatures are monitored and maintained by thermocouples and appropriate circuitry of the reflow and cleaning apparatus which are well known in the art for the control of air or gas temperature.
The entry isolation zone separates the ambient temperature of the reflow and cleaning apparatus from the elevated temperature of the reflow heating zone. Similarly, the exit isolation zone separates the elevated temperature of the reflow assembly from the ambient temperature of the cleaning and reflow apparatus. The entry and the exit isolation zones function as areas of static atmosphere to isolate the different temperatures of the reflow assembly zones and to achieve and maintain a uniform reflow temperature within the reflow heating zone. Each isolation zone is equipped with an exhaust port to exhaust airborne flux particulates and other contaminants from the reflow assembly to the atmosphere external to the reflow and cleaning apparatus.
The air or inert gas distribution system discharges reflow air or inert gas to the reflow heating zone and includes blowers disposed above and below the reflow conveyor. The blowers draw air or inert gas through heaters disposed along each side of the reflow conveyor and into side intake ducts coupled to the heaters. The side intake ducts deliver heat and air or inert gas to a plenum disposed above and below the reflow conveyor. Each plenum is uniformly and positively pressurized by the intake of heat and air or gas. The positive pressure in each plenum creates a mixing action whereby heat and air or gas are mixed to create a uniform air or gas reflow temperature. The reflow air or gas is uniformly discharged from each plenum through a multiple number of perforations or through holes in a surface of each plenum which is in facing relation to the reflow conveyor. The plenum disposed above the reflow conveyor discharges air or gas to a top surface of the reflow conveyor and the plenum disposed below the reflow conveyor discharges air or gas to a bottom surface of the reflow conveyor. The discharged air or gas reflows the BGA components and chips contained on the reflow conveyor by convection or the transfer of thermal energy to the BGA components and chips. Discharged air or gas is subsequently recirculated to the heaters and the side intake ducts by the drawing action created by the blowers.
In a version of the present embodiment in which the air or gas distribution system provides only inert gas, such as nitrogen, the delivery of such inert gas purges oxygen from the reflow assembly to create an inert environment. The entry isolation zone and the exit isolation zone are each further equipped with a seal to enhance the function of each zone to isolate the temperature of the reflow heating zone from other zones in the reflow assembly. In addition, each seal minimizes the consumption of inert gas required to maintain an inert atmosphere in the reflow assembly. Each seal also prevents oxygen from entering the reflow assembly and inert gas from exiting the reflow assembly.
The reflow-to-cooling zone of the reflow assembly functions to isolate the elevated temperature of the reflow heating zone from the cooler temperature of the cooling zone. The reflow-to-cooling zone also prevents the transfer of heat and air or gas from one zone to another. The reflow-to-cooling zone may be equipped with an exhausting device to extract airborne flux particulates and other contaminants from the reflow-to-cooling zone. Removal of such contaminants reduces the level of contamination of the BGA components and chips caused by the condensation of such contaminants onto the BGA components and chips in cooler zones of the reflow assembly.
The cooling zone of the reflow assembly is equipped with at least one blower disposed above the reflow conveyor. The blower discharges cool air drawn from the ambient atmosphere of the reflow and cleaning apparatus to the top surface of the reflow conveyor to cool the BGA components and chips contained on the reflow conveyor. Similarly, a second blower may be disposed below the reflow conveyor to discharge cool air to the bottom surface of the reflow conveyor.
In a version of the present embodiment wherein inert gas is circulated by the distribution system, the cooling zone is equipped with a cooling radiator disposed below the reflow conveyor. The cooling radiator is coupled to either a gas knife, blower or other similar device to discharge cool inert gas into the cooling zone. The gas knife or blower draws inert gas from the reflow and cleaning apparatus and over a surface of the cooling radiator to cool the inert gas prior to discharge into the cooling zone. The drawing action of the gas knife or blower increases the effective volume of the inert gas discharged into the cooling zone to cool the BGA components and chips conveyed on the reflow conveyor.
The amount of convection or thermal energy transfer to the BGA components and chips as such components are conveyed through the reflow assembly is dependent upon the temperature of each zone, the convection velocity and the speed at which the components are conveyed through the reflow assembly.